Luke Harding: My name is Luke Harding. I'm a journalist and a writer, and my new book is called "Collusion," and it's about Donald Trump and Russia.

Putin saying that the collapse of the Soviet Union is the world's greatest geopolitical catastrophe, it's a famous quote and essentially I think it's important because Putin is a KGB guy deep down. He sees the world in conspiratorial terms.

There's a phrase for it that they teach you at KGB spy school which is "glavny protivnik," "the main adversary," and the main adversary is America, both in the '60s, '70s, and '80s, and also now in Putin's head that he sees international politics and diplomacy as a zero sum game in which what's bad for America is good for Russia.

And actually he's had a pretty good run recently. He invaded Ukraine, he has staged military intervention in Syria, and obviously he hacked the US election to help Donald Trump, who I think to Putin's surprise became president.

For Putin, lying is something he does all the time and there's nothing shameful about it. He views lying as a kind of operational tactic, and again it's something he learned about at spy school. You lie for strategic reasons.

But what's astonishing is that Donald Trump seemingly believes Vladimir Putin, the KGB officer, over all 13 US intelligence agencies who unanimously say that Russia hacked the election.

Now, I'm not a psychologist, I can't explain what's going on in Donald Trump's head, but clearly Putin is lying and for Trump to believe him or at least to say he believes him is an astonishing sign of where we now are.

I think he intends to carry on forever. There's a Russian election next year in 2018, but it's like an "election," it's not an election. It's essentially decorative. I think we all know who's going to win it, which means that he'll have another six year term taking him until 2024.

And the logic of this kind of corrupt system in Russia means that he has to carry on forever. And so I can see Putin outlasting Trump, and I think he is going to be a kind of formidable challenge for politicians, not just now but also in the future.